Electronic Article Surveillance (“EAS”) systems are detection systems that allow the detection of markers or tags within a given detection region. EAS systems have many uses. Most often EAS systems are used as security systems to prevent shoplifting from stores or removal of property from office buildings. EAS systems come in many different forms and make use of a number of different technologies.
Typical EAS systems include an electronic detection EAS unit, markers and/or tags, and a detacher or deactivator. The detection unit includes transmitter and receiver antennas and is used to detect any active markers or tags brought within the range of the detection unit. The antenna portions of the detection units can be, for example, bolted to floors as pedestals, buried under floors, mounted on walls, or hung from ceilings. The detection units are usually placed in high traffic areas, such as entrances and exits of stores or office buildings. The deactivators transmit signals used to detect and/or deactivate the tags.
The markers and/or tags have special characteristics and are specifically designed to be affixed to or embedded in merchandise or other objects sought to be protected. When an active marker passes through the detection unit, the alarm is sounded, a light is activated, and/or some other suitable control devices are set into operation indicating the removal of the marker from the proscribed detection region covered by the detection unit.
Most EAS systems operate using the same general principles. The detection unit includes one or more transmitters and receivers. The transmitter sends a signal at defined frequencies across the detection region. For example, in a retail store, placing the transmitter and receiver on opposite sides of a checkout aisle or an exit usually forms the detection region. When a marker enters the region, it creates a disturbance to the signal being sent by the transmitter. For example, the marker may alter the signal sent by the transmitter by using a simple semiconductor junction, a tuned circuit composed of an inductor and capacitor, soft magnetic strips or wires, or vibrating resonators. The marker may also alter the signal by repeating the signal for a period of time after the transmitter terminates the signal transmission. This disturbance caused by the marker is subsequently detected by the receiver through the receipt of a signal having an expected frequency, the receipt of a signal at an expected time, or both. As an alternative to the basic design described above, the receiver and transmitter units, including their respective antennas, can be mounted in a single housing.
Magnetic materials or metal, such as metal shopping carts, placed in proximity to the EAS marker or the transmitter may interfere with the optimal performance of the EAS system. Further, some unscrupulous individuals utilize EAS marker shielding, such as bags lined with metal foil, with the intention to shoplift merchandise without detection by an EAS system. The metal lining of these bags can shield tagged merchandise from the EAS detection system by preventing an interrogation signal from reaching the tags or preventing a reply signal from reaching the EAS system. When a shielded marker passes through the detection unit, the EAS system is not able to detect the marker. As a result, shoplifters are able to remove articles from stores without activating an alarm.
Metal detection systems are used in conjunction with EAS systems to detect the presence of metal objects, such as foil lined bags. The EAS systems and the metal detection systems operate at different energizing frequencies to prevent interference between the systems. For example, the EAS systems and the metal detection systems may use operating frequencies that are separated by 2 kHz.
The metal detection system may use common transmitters and receivers with the EAS system. For metal detection, the transmitter sends a signal across the detection region at a predefined metal detection frequency. When a metal object enters the detection region, it creates a disturbance to the signal being sent by the transmitter. This disturbance caused by the metal object is subsequently detected by the receiver through the receipt of a modified signal. Upon detection of the modified signal, an alarm is sounded, a light is activated, and/or some other suitable control devices are set into operation indicating the presence of metal in a detection region.
EAS/metal detection systems may include a number of metal detectors. Shopping malls or other dense shopping environments may have multiple, separate and independent EAS/metal detection systems in different stores. These EAS/metal detection systems generally operate in an unsynchronized state with respect to the metal detection function.
Conventional metal detection systems generate metal detection signals having a same time duration as the EAS signals. If adjacent unsynchronized metal detection transmission coils are placed in close proximity, the metal detection signal bursts from the adjacent systems may overlap and cause false alarms. What is needed is a system and method that minimizes the occurrence of false alarm signals due to metal detection signal bursts originating from adjacent metal detection system.